Impact of tumor necrosis factor inhibitors and methotrexate on diabetes mellitus among patients with inflammatory arthritis

Abstract

Background: To determine whether initiation of a tumor necrosis factor inhibitor (TNFi) or methotrexate improves hemoglobin A1c in patients with psoriatic arthritis (PsA), rheumatoid arthritis (RA), or ankylosing spondylitis (AS) who also have diabetes mellitus (DM). Methods: A retrospective cohort study was conducted in Optum's de-identified Clinformatics® Data Mart Database, an administrative claims database, using data from 2000 to 2014. Patients with PsA, RA, or AS, with DM (defined by ICD-9-CM codes) and/or HbA1c ≥7%, who newly initiated either a TNFi, MTX, or metformin (positive control) were identified. The change in HbA1c after drug initiation was calculated. Statistical differences in the change in HbA1c between drugs were assessed using the Wilcoxon rank sum test and linear regression models adjusting for potential confounders. Results: Among 10,389 drug initiations in 9541 patients with PsA, RA, or AS, and available HbA1c values, HbA1c was ≥7 at baseline in 254 (35%) TNFi initiations, 361(37%) MTX initiations, and 2144 (50%) metformin initiations. Median HbA1c change was - 0.35 (IQR -1.10, 0.30) after TNFi initiation, - 0.40 (IQR -1.20, 0.30) after MTX initiation, and - 0.80 (IQR -1.60, - 0.10) after metformin initiation. In adjusted analyses, TNFi initiators had less of a decrease in HbA1c compared to MTX initiators (β 0.22, 95% CI: 0.004, 0.43), p = 0.046. Metformin initiators had a significantly greater decrease in HbA1c than MTX, β - 0.38 (95% CI: - 0.52, - 0.23), p < 0.001. Glucocorticoid use was not accounted for in the models. Conclusion: HbA1c decreased with TNFi initiation or MTX initiation. Reductions in HbA1c after initiation of a TNFi or MTX are about half (~ 0.4 units) the decrease observed after initiation of metformin.